During internal combustion piston engine operation, the piston moves between a bottom dead center (BDC) and a top dead center (TDC) position. When operating near the TDC position, depending on various parameters, there may be physical interference between the engine's valves and the piston.
U.S. Pat. No. 6,230,675 describes one situation where such interference can occur. In this example, variation in valve opening timing is combined with a low and high lift cam. Here, the potential interference is addressed by limiting the advancing of the valve opening timing only when a large valve lift is selected. Further, the limiting occurs only when valve control unit is activated and the system is in a high speed mode.
The inventors herein have recognized a disadvantage with such an approach. In particular, the system always limits the advancing of the cam. However, there may be conditions where advancing the cam without limitation, but limiting valve lift, may provide improved performance or increased fuel economy. In addition, whether the valve timing or whether the valve lift should be limited can depend on various factors, such as which actuator has a faster or slower response rate/delay. Furthermore, additional actuators can also influence the potential interference, such as variable compression ratio.
The inventors herein have also recognized that the approach of '675 involves situations where there is an actuator failure. However, potential interference can occur even when both actuators are functional, yet one is moving faster or slower than another during transient conditions.